Many different types of headsets have been designed by numerous manufacturers with various types of end user application in mind. For example, stereo headphones for listening to music have been around for many years, as have ear pieces for use with hearing aids, portable radios such as GB 1,483,829A, U.S. Pat. No. 5,678,202 and U.S. Pat. No. 6,356,644.
Recently, many new types of headset that can be worn by a user have been developed with a view to using them with mobile cellular telephones or other portable electronic devices. Numerous headset designs have been created to enable a user to use such a portable electronic device without the need to hold the electronic device: the so-called “hands-free” mode of operation.
Many of the recently developed headsets are cordless devices that incorporate a Bluetooth™ receiver or a Bluetooth™ receiver/transmitter. Bluetooth™ is a radio-frequency communications standard developed by a group of electronics manufacturers that allows various types of electronic equipment to interconnect, without the need for wires, cables or detailed user intervention. The Bluetooth™ standard enables various electronic devices to inter-operate, since all electronic products that use Bluetooth™ have to use an agreed standard that dictates when data bits are sent, how many data bits are sent at any one time, how data transmission errors are handled, etc.
Whilst improved design has lead to improvements in the size and weight of headsets, the functionality of headsets has increased dramatically. This has increased pressure on engineers to consider how most efficiently to use the electrical power available, particularly for cordless battery-operated headsets where battery life and available power are limited.
With a view to improving power usage, various manufacturers have developed headsets that incorporate power management features.
One prior art design is that of the Sony™ MDR-DS8000 headset available from Sony™ Corporation. In this headset, an electromechanical switch is provided that changes state when the ear pieces are pulled apart when the headset is being put on by a user. This is done by the headband expanding and pulling on a switch mechanism.
In another prior art design JP2000278785 A, an inductive noise signal is provided by a metallic ring built into an ear piece when the ear piece contact a user. This signal is used to detect the presence or absence of a user to determine whether or not to power-down a signal amplifier.
While these known power-saving headsets fulfil the desired function, they are not without various drawbacks. For example, mechanical switches are relatively bulky and expensive, and they can also suffer from long-term reliability problems. Moreover, the mechanical headband switch approach is not transferable to non-headband based headsets such as single-ear devices, for example ones that operate wirelessly by Bluetooth™ or otherwise. Sensing user presence based upon detecting inductive noise is also less than ideal, particularly given the random nature of such noise and its amplitude variability according to differing physical conditions, such as the degree of electrode contact with the user (e.g. if a user is jogging), prevailing environmental conditions (e.g. if a user is sweating or is exposed to rain), etc.